black pixels in render

[Valentina]

Hi, I post here my second real project (yes I'm really new in Terragen). With "real" I mean : not just a casual play but something I'm really focused on. The tgd file is a couple of months old, my first at all, I produced some awful renders, then I started working with more brain with tutorials and so on.. now, I've put again my hands on it. Problem is, it used to give me no black pixels at all in renders, why now it does? now every render I make is "pixeled".. yes, it's not very good, but with those blak dots...... even worse.

Any suggestion? If allowed to, I can add the tgd file.


Any critics or suggestion about the scene is welcome of course..

[attachimg=1]

[Kadri]

If you want you can share your file here.
Sometimes it is the best way to see what is wrong.
The first that comes to my mind is too much displacement.

[Valentina]

thank you for your answer,
in the terrain tab, I unchecked the "small details" terrain and i obtained black pixels too. without that layer, that tab was the same as the previous file (the one of no black dots). new are also the shaders in this file..

here is the tgd file..

[Dune]

Kadri is right; the ridged fractal and the fractal warp don't work pleasantly together, resulting in too much displacement. Best to change the roughness of the fractal warp to 0.9 (it's now at 1) and move the small detail beyond compute terrain. Then it should be fine.

[Valentina]

.. M.. Ok.. Really thank you.. I think i need to process this answer! There are the subject and the language 
Thank you again! I'll lte you know
Valentina

EDIT
maybe I've not done in the right way this "move the small detail beyond compute terrain", but  still get black pixels..

[Kadri]

Valentina and Ulco, as i said i thought it was the displacement probably.
But it looks like the Grass nodes are the real reason interestingly.
Not sure what is going on. I haven't looked and tried everything.
But with only the last Grass node active you get no black parts for example.
It might be only a color thing maybe, because even with zero displacement in the grass nodes there were still black parts.

[Valentina]

Maybe too many grass  nodes "stress" my pc? That i have to say, can render products and room scenes.. Because these black spots are like the ones that i can see during the prepass before the final rendered image.. Like a quality issue? Because it really seems like it doesn't really 'end' to render.. I don't know if i am able to explain What i mean..

In my firts tg project there where 4 or 5 shaders, i'll try here with only One grass node, Let's see. Thank you
Valentina


Edit: ok if you have black spots too, no problem of quality or pc i guess..

[Kadri]

This is only related to the settings-nodes in Terragen. It is not a PC problem.
Use a basic green grass node for example and you will see no black parts i think.

[Valentina]

Ok...! I like What comes out using different grass nodes with different colors, but black spots.. Those, are awful. So i will follow your advice and let's see, many thanks

[Matt]

The black spots are caused by colours with negative values, i.e. colours darker than black. This is happening in some of your grass shaders. To find this out, I disabled the grass shaders and enabled them one-by-one until the black spots reappeared.

In your setup the grass surfaces each have a "fractal breakup" shader connected to the "colour function" input. This means that the grass shader's colour is multiplied by the value of the fractal breakup shader. It is OK to connect the shaders this way but you need to be careful about negative values. The "fractal breakup" nodes have the potential to create negative values in some places because the output isn't clamped. You can fix this by going to the "Colour" tab on each of the fractal breakup shaders and enabling "Clamp low colour":



However, if you enable clamping it might also change the distribution of your grass surfaces because you are using the same node to affect the colour and the coverage (fractal breakup) of the surface. There are other ways you can clamp the output of the fractal shader, e.g. using a "Clamp 0 colour" node. If you do that, you can clamp it for colour purposes while using the non-clamped value for the fractal breakup.

Matt

[Valentina]

Thank you Matt, really. I've understood!!

Thank you for your time and patience.. (Thank you all, actually)

[Kadri]

Thanks Matt.Good to know.I think i didn't saw this before.